Queues

// FIFO

class Node{
   late dynamic value;
   late dynamic next;
    Node(value){
        this.value = value;
        this.next = null;
        
    }
}

class Queue{
   late dynamic first;
   late dynamic last;
   late int length;
    Queue(){
        this.first = null;
        this.last = null;
        this.length = 0;
    }
    
    // add at the back of last 
    enQueue(value){
        Node newNode = new Node(value);
    if(length == 0){
        first = newNode;
        last = first;
        
    }else{
        
        last.next = newNode;
        last = newNode;
       
    }
    length++;
    
}

// remove the first push
    deQueue(){
     if(first == last){
         return first;
     } else if(first == null){
         return null;
     }else{
        first = first.next;
     }
        length--;
    }
    
    // return the top;
    peek(){
        return first!= null? first.value.toString(): 'empty';
    }
    
    @override
    String toString(){
       List<dynamic> values = [];
    Node? current = first;
    while (current != null) {
      values.add({
      'value': current.value,
      'next': current.next?.value,
     
    });  // Add only values
      current = current.next;
    }
    
    
      'length': length,
      'elements': values
    } .toString();
  
    }
}



void main() {
    Queue queue = new Queue();
    queue.enQueue(23);
    queue.enQueue(25);
    queue.enQueue(26);
    // queue.enQueue(27);
    // queue.enQueue(28);
    // queue.enQueue(29);
    // queue.enQueue(24);
      print(queue);
    queue.deQueue();
    print( queue.peek());
    print(queue);
}